1. Technical Field
The present invention relates to an image processor, an image processing method, a printer, a printing method, a program, and a recording medium, which can suppress the occurrence of banding such as a white line or dark line due to a flying bend in a nozzle during printing by discharging ink from the nozzle.
2. Related Art
There has been known a printer that has a recording head for discharging ink, and performs printing by forming dots on a medium such as paper, cloth and plastic, or a transparency (hereinafter, simply called recording paper) by discharging the ink to the medium.
This type of printer is configured in a manner that a plurality of nozzles are formed in the recording head, and ink is discharged from the nozzles, however, in one or more of the nozzles, a discharge direction of the ink may be deflected, causing a shift in the landing position of a dot, and a so-called flying bend may occur. In this case, there is a problem that, for example, when a uniform pattern image is printed, a white line (so-called banding) appears in a printed image, which degrades printing quality.
Hereinafter, a printer, particularly a printer employing an inkjet method (hereinafter, referred to as “inkjet printer”) is described.
Generally, inexpensive and high-quality color prints are easily obtained from inkjet printers and therefore inkjet printers have been widely used not only at an office but also by a general user with the widespread use of personal computers and digital cameras.
Such an inkjet printer is typically formed in a way that a movable body called carriage, which integrally includes an ink cartridge and an ink head, discharges (ejects) particles of liquid ink in a dotted form from nozzles in the printing head while reciprocating across a printing medium (paper) in a direction perpendicular to a feed direction relative to the paper, thereby predetermined letters or images are drawn on the printing medium to make a desired print. The carriage typically includes ink cartridges of four colors including black (black, yellow, magenta, and cyan) and printing heads for respective colors, so that not only monochrome printing but also full-color printing can be easily carried out by combining respective colors (furthermore, a printer of six colors, seven colors, or eight colors formed by adding light cyan, light magenta and the like to the colors is now practically used).
In such an inkjet printer (where the printing head on the carriage performs printing while reciprocating in the direction perpendicular to the paper feed direction), since the printing head needs to be reciprocated dozens of times to one hundred times or more to finely make prints on a full page, there is a drawback in that an extremely long printing time is required as compared with other types of printers such as a laser printer using an electrophotographic technique like a copier. This type of inkjet printer is generally called a “multipass printer” or “serial printer”.
On the contrary, in an inkjet printer with a long-size printing head having a size equal to (or longer than) the width of the printing paper disposed so that a carriage is not used, the printing head need not be moved in a lateral direction relative to the printing paper, and a so-called one scan (one pass) printing is possible, therefore high-speed printing similar to a laser printer is possible. Moreover, since a carriage for mounting the printing head and a drive system for moving the carriage are not necessary, a chassis of the printer can be reduced in size and weight, and furthermore quietness is remarkably improved. This type of inkjet printer is generally called a “line head printer”.
Since a printing head indispensable for such an inkjet printer is formed by arranging small nozzles 10 to 70 μm in diameter in one line with a constant interval or arranging the nozzles in several lines in a printing direction, the discharge directions of ink from some nozzles may be deflected due to manufacturing errors, or a position of the nozzle may be disposed at a position shifted from an ideal position. Consequently a so-called “flying bend phenomenon” such as a phenomenon that the landing positions of dots formed by the nozzle may be shifted from target points may occur.
As a result, a printing defect, known as a so-called “banding (line) phenomenon” may occur, which sometimes significantly reduces printing quality. That is, once the “flying bend phenomenon” occurs, a “white line (in the case of a white printing paper)” appears at a portion where a distance between dots discharged from adjacent nozzles is large, and a “dark line” appears at a portion where the distance between dots discharged from adjacent nozzles is short.
In particular, such a banding phenomenon tends to occur more significantly in the “line head printer” where the printing head or the printing medium is fixed (one pass printing) as compared with the case of the “multi-pass printer” (serial printer) (in the multi-pass printer, there is a technique of making the banding relatively inconspicuous by reciprocating the printing head many times).
Therefore, to prevent a kind of, printing defect due to such a “banding phenomenon”, research and development in hardware, such as improvement in manufacturing or improvement in the design of the printing head are earnestly pursued, however, it is difficult in view of manufacturing cost or technology to provide a printing head in which the “banding phenomenon” does not occur 100% of the time.
Thus, in addition to the improvement in the hardware, technology for reducing such a “banding phenomenon” using a so-called software method such as the following printing controls is now combined.
To solve the problem, a technique is proposed, in which dark and light, that is, two types of ink including dark ink having high dye concentration and light ink having a lower dye concentration than that of the dark ink and high permeability, are provided, and dots are formed using the light ink in the whole halftone (for example, refer to JP-A-11-48462). According to the technique, the high permeability of the light ink causes bleeding and consequently a dot larger in size than a dot to be essentially formed is formed. Therefore, even if the landing position of the dot is shifted particularly due to the flying bend, a blank space caused by shifting of the position can be compensated, and consequently the occurrence of the white line can be suppressed (for example, refer to JP-A-11-48462 (FIG. 1)).
However, there has been a problem in the related art that since the light ink is used in the full halftone range, and thus comparatively large dots are formed, respective dots become easily visible, and consequently a granular feeling of a printed image is increased.
Furthermore, there is a problem that since the high permeability of the light ink is used for suppressing the occurrence of the white line, ink having low permeability such as pigment ink can not be used.